The present invention relates generally to power supplies for electronic systems, and more particularly to efficient operation of charge pumps, which are commonly used in such power supplies, by controlling the transitioning of such charge pumps between multiple modes of operation.
Electronic circuits today often require power in one or more direct current (DC) voltage ranges. To supply such needs it is typical to convert power from a single source, perhaps a battery or another DC supply already obtained from an alternating current source. Various systems exist for performing such power conversion, including the charge pump. A charge pump is a capacitor and oscillator based circuit which converts a DC input to a DC output which is either higher, lower, or inverted in voltage value.
FIG. 1a (background art) is a circuit diagram of a very simple charge pump. An oscillator (OSC) controls two switches (S1 and S2) to alternately charge a flying capacitor (Cx) from an input voltage (VIN) supplied across an input capacitor (CIN), and to discharge the flying capacitor (Cx) into an output capacitor (COUT). The voltage thus produced across the output capacitor becomes an output voltage (VOUT). The oscillator, switches, and still other controls are all commonly contained in an integrated circuit (IC) today.
The charge pump in FIG. 1a is of the step-up type, and it operates by stacking the potential of the charge in the flying capacitor onto the potential of the input, and then charging the output capacitor with this. The optimal result of this is an output voltage which is double that of the input voltage.
Those skilled in the electronic arts will readily appreciate that switched connections to the flying capacitor can be changed to simply shift charge from the input to the output, rather than to stack it as above. One very common type of step-down charge pump operates in this way, but further includes an appreciable resistance in the charge path to the flying capacitor. The resistance intentionally introduces a delay in the charging of the flying capacitor, and appropriate control of the oscillator is then used to switch the charge before it is able to reach the full input voltage potential. This type of charge pump may accordingly transfer charge quanta having only one-half, two-thirds, etc. of the input voltage, and thereby produce an output voltage which is correspondingly lower than the input voltage. This type of step-down charge pump is probably overwhelmingly the most common today, but it is not the only type possible.
FIG. 1b (background art) is a circuit diagram of a less common type of step-down charge pump. An oscillator (OSC) controls switches (here S1, S2, and S3) to alternately charge two flying capacitors (C1 and C2) from an input voltage (VIN) which is supplied across an input capacitor (CIN). For charging, the two flying capacitors are connected in series by the switches across the input capacitor. However, for discharging, the two flying capacitor are each connected in parallel by the switches across an output capacitor (COUT). This accordingly produces an output voltage (VOUT), but one which is nominally only one-half that of the input voltage. Since the two flying capacitors are charged in series to the total input voltage, so that they each reach roughly half of that voltage, this is all of the potential that either can subsequently contribute toward creating the output voltage. FIG. 1b depicts the switches set for the discharge cycle of this process.
Several dynamic conditions may occur in electronic circuits, and it may be necessary or desirable for a charge pump to adapt conversion of a DC input to a DC output differently in response to such conditions. For example, the input voltage can change. If a battery is used for the input, simple battery discharge will cause the input voltage to drop. Or the output load may change, creating a need to supply increased charge quanta to the output capacitor to prevent the output voltage from dropping too low, i.e., dropping out of regulation.
Constructing charge pumps which are capable of transitioning between different operating modes is not particularly difficult. Some common examples of this are charge pumps which alternately perform either step-up or step-down conversion (sometimes also respectively called boost and buck operation), as needed, or charge pumps which alternately switch between step-up multiples of the input voltage, e.g., from 2x to 3x modes.
Unfortunately, providing charge pumps which can operate in multiple such modes efficiently is not easily accomplished. Inefficiency is generally undesirable, and it can be a severe limitation when using charge pumps with battery and other limited power sources. Accordingly, what is needed are improved systems, apparatus, and methods for providing efficient multiple mode charge pumps.
Accordingly, it is an object of the present invention to provide a transitioning system for efficient multiple mode operation of charge pumps.
Another object of the invention is to provide a transitioning system for multiple mode operation of charge pumps which works efficiently across a wide range, and preferably the total range, of appropriate output loads likely to be encountered by particular circuits employing the charge pumps.
Another object of the invention is to provide;a transitioning system for multiple mode operation of charge pumps which maintains high efficiency and high output current capability consistently.
And another object of the invention is to provide a system for multiple mode operation of charge pumps which transitions automatically between such modes in a manner supplying high efficiency or high output current, as may be appropriate for particular output loads.
Briefly, one preferred embodiment of the present invention is a method for operating a charge pump to convert an input voltage in an input signal to an output voltage in an output signal. The charge pump includes an oscillator which produces clock cycles and a number of flying capacitors which are charged during first half clock cycles and discharged during the other half clock cycles. The method operates the charge pump for at least one clock cycle in a first step mode defined by particular interconnection and combination of the flying capacitors both while they are charged and discharged. Next it is determined if the charge pump is within regulation, based upon whether the output voltage is within a desired range. Then the input voltage and the output voltage are compared to determine if the charge pump can operate in a second step mode, which is defined by a different unique interconnecting combination of the flying capacitors as they are first charged and then discharged. Finally, the charge pump may transition from operation in the first step mode to operation in the second step mode if it is in regulation and if it is also determined that it can operate in the second step mode.
An advantage of the present invention is that it does provide an efficient, automatically operating transitioning system for multiple mode operation of charge pumps, one able to accommodate a full range of charge pump input conditions and output loads.
Another advantage of the present invention is that it may be largely monolithically implemented. The invention may be incorporated into monolithic integrated circuit type charge pump designs without the need for additional discrete components or resorting to non-monolithic assemblies. Yet the invention may also use discrete components or non-monolithic assemblies, or be integrated into charge pump designs which use such for other purposes, if a designer so wishes.
Another advantage of the present invention is that it may be implemented using widely understood and economical integrated circuit digital logic.
And another advantage of the invention is that it also reduces output voltage ripple when the output voltage is close to the input voltage at light and medium output load currents.
These and other objects and advantages of the present invention will become clear to those skilled in the art in view of the description of the best presently known mode of carrying out the invention and the industrial applicability of the preferred embodiment as described herein and as illustrated in the several figures of the drawings.